Sarath D. Perera

Synthesis and reactions of ene–hydrazone diphosphine iridium complexes and related species†

Treatment of the azine diphosphine Z,Z-PPh2CH2C(But)N–NC(But)CH2PPh2 I with [IrCl(CO)2(H2NC6H4Me-4)] in benzene gave the ene–hydrazone diphosphine iridium(III) hydride [IrH(Cl)(CO){PPh2CHC(But)N–NC(But)CH2PPh2}], 1, which isomerised reversibly to the ionic square planar iridium(I) complex [Ir(CO){PPh2CH2C(But)N–NC(But)CH2PPh2}]Cl 2a, containing an azine diphosphine. Treatment of 1 with NEt3 gave the neutral ene–hydrazone diphosphine iridium(I) complex [Ir(CO){PPh2CHC(But)N–NC(But)CH2PPh2}] 3 which is reactive and undergoes oxidative addition of H2 to give the iridium(III) dihydride mer,cis-[IrH2(CO){PPh2CH C(But)N–NC(But)CH2PPh2}] 4 and oxidative addition of MeI to give the methyliridium(III) complex [IrMe(I)(CO){PPh2CHC(But)N–NC(But)CH2PPh2}] 5. It reacted rapidly with olefins or acetylenes (L), i.e.N-methylmaleimide, ethene or dimethyl acetylenedicarboxylate, to give the five-co-ordinate adducts [Ir(CO)L{PPh2CH C(But)N–NC(But)CH2PPh2}], 6a, 6b or 6c, respectively, also with O2 to give the η2-dioxygen adduct [Ir(CO)(η2-O2){PPh2CHC(But)N–NC(But)CH2PPh2}] 7. Treatment of 3 with 1 mol of picric acid protonated the ene–hydrazone diphosphine backbone to give the azine diphosphine iridium(I) salt [Ir(CO){PPh2CH2C(But)N–N C(But)CH2PPh2}][OC6H2(NO2)3] 2b. The N-methylmaleimide adduct 6a was similarly protonated to give the corresponding azine diphosphine iridium(I) salt [Ir(CO)(η2-COCHCHCONMe){PPh2CH2C(But)N–NC(But)CH2PPh2}][OC6H2(NO2)3] 8. Complex 1 was protonated by HCl to give the corresponding azine diphosphine iridium(III) salt [IrH(Cl)(CO){PPh2CH2C(But)N–NC(But)CH2PPh2}]Cl 9a, which is converted into 3 when treated with NEt3. The 1H, 13C and 31P NMR and some IR data are given.

Novel chemistry of rhodium induced by a new type of ligand, aphosphino-N-benzoylhydrazone: crystal structure of[Rh(CO){C(CO2Me)CHCO2Me}{PPPh2CH[C(CO2Me)C (CO2Me)]C -(But)N –NC(Ph)O }]

Treatment of the phosphino-N,N-dimethylhydrazone Z-PPh 2 CH 2 C(Bu t )NNMe 2 with benzohydrazide in the presence of acetic acid gave the phosphino-N-benzoylhydrazone PPh 2 CH 2 C(Bu t )NNHC(O)Ph I. Treatment of the phosphine I with 0.5 equivalent of [{RhCl(CO) 2 } 2 ] gave the rhodium(I) complex [Rh(CO){PPh 2 CH 2 C(Bu t )N–NC(Ph)O}] 1 containing two fused five-membered chelate rings. Complex 1 readily reacted with Br 2 to give the dibromorhodium(III) complex [RhBr 2 (CO){PPh 2 CH 2 C(Bu t )N–NC(Ph) O }] 2. Similarly, it underwent oxidative-addition reactions with MeI or HCCCH 2 Cl to give rhodium(III) complexes of type [RhX(R)(CO){ PPh 2 CH 2 C(Bu t ) N–NC(Ph) O }] (R = Me, X = I 3; R = CHCCH 2 , X = Cl 4). In contrast, treatment of 1 with allyl bromide caused loss of the carbon monoxide ligand to give the η 3 -allylrhodium(III) complex [RhBr(η-3-C 3 H 5 ){ PPh 2 CH 2 C(Bu t )  N–NC(Ph)O }] 5. Treatment of 1 with MeO 2 CCCCO 2 Me gave the cyclometallated alkenylrhodium(III) complex [Rh(CO){C(CO 2 Me)CHCO 2 Me }{ PPh 2 CH[C(CO 2 Me) C(CO 2 Me)]C(Bu t )  N–NC(Ph)O }] 6, in which the phosphine ligand is tetradentate through P, N, O and C; in the formation of 6 one alkyne has attacked the methylene carbon of the phosphine ligand and the second has added to Rh–H to give RhC(CO 2 Me)CH(CO 2 Me). On the prolonged heating 6 isomerised to give the rhodium(III) complex 7; in this isomer the C(CO 2 Me)CH(CO 2 Me) ligand is trans to phosphorus whereas in 6 it is cis. The crystal structure of 6 has been determined.

[2 + 2 + 2] cyclotrimerisation as a convenient route to 6N-doped nanographenes: a synthetic introduction to hexaazasuperbenzenes

6N-containing polyphenylene precursors were generated via [2 + 2 + 2] cyclotrimerisation. On methoxy substitution complete ring-closure can be achieved (via FeCl3-mediated oxidative cyclodehydrogenation) to give asymmetric and C3v symmetric hexaazasuperbenzenes. Investigations using DDQ/H+ mediated conditions reveal this to be a promising alternative and selective route to partial cyclodehydrogenation.

Thiophene Containing Polyaromatic Hydrocarbons

In this poster we detail recent investigations into the formation of new sulfur-based polyaromatic hydrocarbons. These form an extension to our previous work on a new class of polyaromatic, nitrogen-containing compounds, the “N-Heterosuperbenzenes”. Through modification of our developed synthetic str ategy we have successfully incorporated thiophene rings into the periphery of the polyphenyl precursors and studied their influence on key chemical modifications such as dehydrogenation, carbon-carbon bond formation and polymerisation. Building on the work of Tovar and McCullough we show the unique consequences of steric bulk in t he polyphenylene precursor; and examine how changes in the dehydrogenation conditio s alter the aromaticity of the final products. Strategies to control the polymerisation and dimerisation reactions of the precursors have been developed. Investigations into the photochemical and electrochemical properties of the precursors and th e new fused aromatics will be presented along with their possible application in metal coordination complexes and molecular switching devices.

Macropolyhedral boron-containing cluster chemistry: isolation andcharacterization of twenty-one-vertex[(PMe2Ph)3HReB20H15Ph(PHMe2)]

Reaction of B 20 H 16 with [ReH 5 (PMe 2 Ph) 3 ] yields the twenty-one-vertex metallaborane [(PMe 2 Ph) 3 HReB 20 H 15 Ph- (PHMe 2 )] which consists of a closo twelve-vertex {B 12 } unit and a nido eleven-vertex {B 11 } unit fused with a common triangular face, with the {(PMe 2 Ph) 3 HRe} moiety capping exo to the nido {B 11 } unit with three Re–H–B bonds; an unusual reductive P-phenyl cleavage of a PMe 2 Ph moiety to give B-pendant exo PHMe 2 and exo Ph moieties on the open face of the eleven-vertex subcluster is also apparent.